「干货」如何从0写一个服务网关？

java程序媛之家一个有深度程序媛公众号一、引 言什么是网关？为什么需要使用网关？

如图所示，在不使用网关的情况下，我们的服务是直接暴露给服务调用方当调用方增多，势必需要添加定制化访问权限、校验等逻辑当添加API网关后，再第三方调用端和服务提供方之间就创建了一面墙，这面墙直接与调用方通信进行权限控制。

本文所实现的网关源码抄袭了—Oh,不对，是借鉴借鉴了Zuul网关的源码，提炼出其核心思路，实现了一套简单的网关源码，博主将其改名为Eatuul题外话本文是业内能搜到的第一篇自己动手实现网关的文章博主写的手把手系列的文章，目的是在以最简单的方式，揭露出中间件的核心原理，让读者能够迅速了解实现的核心。

需要说明的是，这不是源码分析系列的文章，因此写出来的代码，省去了一些复杂的内容，毕竟大家能理解到该中间件的核心原理即可如果想看源码分析系列的，请关注博主，后期会将spring、spring boot、dubbo、mybatis等开源框架一一揭示。

二、正 文设计思路先大致说一下，就是定义一个Servlet接收请求然后经过preFilter(封装请求参数),routeFilter(转发请求)，postFilter(输出内容)三个过滤器之间，共享request、response以及其他的一些全局变量。

如下图所示

和真正的Zuul的区别?主要区别有如下几点(1)Zuul中在异常处理模块，有一个ErrorFilter来处理，博主在实现的时候偷懒了，略去(2)Zuul中PreFilters,RoutingFilters,PostFilters默认都实现了一组，具体如下表所示。

博主总不可能每一个都给你们实现一遍吧所以偷懒了，每种只实现一个但是调用顺序还是不变，按照PreFilters->RoutingFilters->PostFilters的顺序调用(3)在routeFilters确实有转发请求的Filter,然而博主偷天换日了，改用RestTemplate实现.。

代码结构大家去spring官网上搭建一套springboot的项目，博主就不展示pom的代码了。直接将项目结构展示一下，如下图所示

EatuulServlet.java这个是网关的入口，逻辑也十分简单，分为三步(1)将request,response放入threadlocal中(2)执行三组过滤器(3)清除threadlocal中的的环境变量

源码如下package com.rjzheng.eatuul.http; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; @WebServlet(name = “eatuul”, urlPatterns = “/*”) public class EatuulServlet extends HttpServlet { private EatRunner eatRunner = new EatRunner(); @Override public void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //将request，和response放入上下文对象中 eatRunner.init(req, resp); try { //执行前置过滤 eatRunner.preRoute(); //执行过滤 eatRunner.route(); //执行后置过滤 eatRunner.postRoute(); } catch (Throwable e) { RequestContext.getCurrentContext().getResponse() .sendError(HttpServletResponse.SC_NOT_FOUND, e.getMessage()); } finally { //清除变量 RequestContext.getCurrentContext().unset(); } } }

EatuulRunner.java这个是具体的执行器需要说明一下，在Zuul中，ZuulRunner在获取具体有哪些过滤器的时候，有一个FileLoader可以动态读取配置加载博主在实现我们自己的EatuulRunner时候，略去动态读取的过程，直接静态写死。

源码如下package com.rjzheng.eatuul.http; import java.util.ArrayList; import java.util.List; import java.util.concurrent.ConcurrentHashMap; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.rjzheng.eatuul.filter.EatuulFilter; import com.rjzheng.eatuul.filter.post.SendResponseFilter; import com.rjzheng.eatuul.filter.pre.RequestWrapperFilter; import com.rjzheng.eatuul.filter.route.RoutingFilter; public class EatRunner { //静态写死过滤器 private ConcurrentHashMap hashFiltersByType = new ConcurrentHashMap(){{ put(“pre”,new ArrayList(){{ add(new RequestWrapperFilter()); }}); put(“route”,new ArrayList(){{ add(new RoutingFilter()); }}); put(“post”,new ArrayList(){{ add(new SendResponseFilter()); }}); }}; public void init(HttpServletRequest req, HttpServletResponse resp) { RequestContext ctx = RequestContext.getCurrentContext(); ctx.setRequest(req); ctx.setResponse(resp); } public void preRoute() throws Throwable { runFilters(“pre”); } public void route() throws Throwable{ runFilters(“route”); } public void postRoute() throws Throwable{ runFilters(“post”); } public void runFilters(String sType) throws Throwable { List list = this.hashFiltersByType.get(sType); if (list != null) { for (int i = 0; i < list.size(); i++) { EatuulFilter zuulFilter = list.get(i); zuulFilter.run(); } } } }

EatuulFilter.java接下来就是一系列Filter的代码了，先上父类EatuulFilter的源码package com.rjzheng.eatuul.filter; public abstract class EatuulFilter { abstract public String filterType(); abstract public int filterOrder(); abstract public void run(); }

RequestWrapperFilter.java这个是PreFilter,前置执行过滤器，负责封装请求步骤如下所示(1)封装请求头(2)封装请求体(3)构造出RestTemplate能识别的RequestEntity。

(4)将RequestEntity放入全局threadlocal之中代码如下所示package com.rjzheng.eatuul.filter.pre; import java.io.IOException; import java.io.InputStream; import java.net.URI; import java.net.URISyntaxException; import java.util.Collections; import java.util.List; import javax.servlet.http.HttpServletRequest; import org.springframework.http.HttpHeaders; import org.springframework.http.HttpMethod; import org.springframework.http.RequestEntity; import org.springframework.util.MultiValueMap; import org.springframework.util.StreamUtils; import com.rjzheng.eatuul.filter.EatuulFilter; import com.rjzheng.eatuul.http.RequestContext; public class RequestWrapperFilter extends EatuulFilter{ @Override public String filterType() { // TODO Auto-generated method stub return “pre”; } @Override public int filterOrder() { // TODO Auto-generated method stub return -1; } @Override public void run() { String rootURL = “http://localhost:9090”; RequestContext ctx =RequestContext.getCurrentContext(); HttpServletRequest servletRequest = ctx.getRequest(); String targetURL = rootURL + servletRequest.getRequestURI(); RequestEntity requestEntity = null; try { requestEntity = createRequestEntity(servletRequest, targetURL); } catch (Exception e) { e.printStackTrace(); } //4、将requestEntity放入全局threadlocal之中 ctx.setRequestEntity(requestEntity); } private RequestEntity createRequestEntity(HttpServletRequest request,String url) throws URISyntaxException, IOException { String method = request.getMethod(); HttpMethod httpMethod = HttpMethod.resolve(method); //1、封装请求头 MultiValueMap headers =createRequestHeaders(request); //2、封装请求体 byte[] body = createRequestBody(request); //3、构造出RestTemplate能识别的RequestEntity RequestEntity requestEntity = new RequestEntity(body,headers,httpMethod, new URI(url)); return requestEntity; } private byte[] createRequestBody(HttpServletRequest request) throws IOException { InputStream inputStream = request.getInputStream(); return StreamUtils.copyToByteArray(inputStream); } private MultiValueMap createRequestHeaders(HttpServletRequest request) { HttpHeaders headers = new HttpHeaders(); List headerNames = Collections.list(request.getHeaderNames()); for(String headerName:headerNames) { List headerValues = Collections.list(request.getHeaders(headerName)); for(String headerValue:headerValues) { headers.add(headerName, headerValue); } } return headers; } }

RoutingFilter.java这个是routeFilter,这里我偷懒了，直接做转发请求，并且将返回值ResponseEntity放入全局threadlocal中package com.rjzheng.eatuul.filter.route; import org.springframework.http.RequestEntity; import org.springframework.http.ResponseEntity; import org.springframework.web.client.RestTemplate; import com.rjzheng.eatuul.filter.EatuulFilter; import com.rjzheng.eatuul.http.RequestContext; public class RoutingFilter extends EatuulFilter{ @Override public String filterType() { // TODO Auto-generated method stub return “route”; } @Override public int filterOrder() { // TODO Auto-generated method stub return 0; } @Override public void run(){ RequestContext ctx = RequestContext.getCurrentContext(); RequestEntity requestEntity = ctx.getRequestEntity(); RestTemplate restTemplate = new RestTemplate(); ResponseEntity responseEntity = restTemplate.exchange(requestEntity,byte[].class); ctx.setResponseEntity(responseEntity); } }

SendResponseFilter.java这个是postFilters,将ResponseEntity输出即可package com.rjzheng.eatuul.filter.post; import java.util.List; import java.util.Map; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServletResponse; import org.springframework.http.HttpHeaders; import org.springframework.http.ResponseEntity; import com.rjzheng.eatuul.filter.EatuulFilter; import com.rjzheng.eatuul.http.RequestContext; public class SendResponseFilter extends EatuulFilter{ @Override public String filterType() { return “post”; } @Override public int filterOrder() { return 1000; } @Override public void run() { try { addResponseHeaders(); writeResponse(); } catch (Exception e) { e.printStackTrace(); } } private void addResponseHeaders() { RequestContext ctx = RequestContext.getCurrentContext(); HttpServletResponse servletResponse = ctx.getResponse(); ResponseEntity responseEntity = ctx.getResponseEntity(); HttpHeaders httpHeaders = responseEntity.getHeaders(); for(Map.Entry entry:httpHeaders.entrySet()) { String headerName = entry.getKey(); List headerValues = entry.getValue(); for(String headerValue:headerValues) { servletResponse.addHeader(headerName, headerValue); } } } private void writeResponse()throws Exception { RequestContext ctx = RequestContext.getCurrentContext(); HttpServletResponse servletResponse = ctx.getResponse(); if (servletResponse.getCharacterEncoding() == null) { // only set if not set servletResponse.setCharacterEncoding(“UTF-8”); } ResponseEntity responseEntity = ctx.getResponseEntity(); if(responseEntity.hasBody()) { byte[] body = (byte[]) responseEntity.getBody(); ServletOutputStream outputStream = servletResponse.getOutputStream(); outputStream.write(body); outputStream.flush(); } } }

RequestContext.java最后是一直在说的全局threadlocal变量package com.rjzheng.eatuul.http; import java.util.HashMap; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.springframework.http.RequestEntity; import org.springframework.http.ResponseEntity; public class RequestContext extends ConcurrentHashMap { protected static Class contextClass = RequestContext.class; protected static final ThreadLocal threadLocal = new ThreadLocal() { @Override protected RequestContext initialValue() { try { return contextClass.newInstance(); } catch (Throwable e) { throw new RuntimeException(e); } } }; public static RequestContext getCurrentContext() { RequestContext context = threadLocal.get(); return context; } public HttpServletRequest getRequest() { return (HttpServletRequest) get(“request”); } public void setRequest(HttpServletRequest request) { put(“request”, request); } public HttpServletResponse getResponse() { return (HttpServletResponse) get(“response”); } public void setResponse(HttpServletResponse response) { set(“response”, response); } public void setRequestEntity(RequestEntity requestEntity){ set(“requestEntity”,requestEntity); } public RequestEntity getRequestEntity() { return (RequestEntity) get(“requestEntity”); } public void setResponseEntity(ResponseEntity responseEntity){ set(“responseEntity”,responseEntity); } public ResponseEntity getResponseEntity() { return (ResponseEntity) get(“responseEntity”); } public void set(String key, Object value) { if (value != null) put(key, value); else remove(key); } public void unset() { threadLocal.remove(); } }

如何测试？自己另外起一个server端口为9090如下所示package com.rjzheng.eatservice; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.boot.builder.SpringApplicationBuilder; import org.springframework.boot.web.servlet.ServletComponentScan; import com.rjzheng.eatservice.controller.IndexController; @SpringBootApplication @ServletComponentScan(basePackageClasses = IndexController.class) public class Application { public static void main(String[] args) { new SpringApplicationBuilder(Application.class).properties(“server.port=9090”).run(args); } }

再来一个controllerpackage com.rjzheng.eatservice.controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; @RestController public class IndexController { @RequestMapping(“/index”) public String index() { return “hello!world”; } }

然后，你就发现可以从localhost:8080/index进行跳转访问了三、结 论本文模拟了一下zuul网关的源码，借鉴了一下其精髓的部分希望大家能有所收获–（完） –看完本文有收获？请转发分享给更多人。

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